The present invention relates to a high-frequency circuit having a built-in dielectric resonator and a oscillator using this high-frequency circuit, and their production method.
In a frequency processing circuit for the high-frequency region such as microwave and extremely high frequency wave, it is required to reduce the phase noise in order to stabilize the frequency characteristic of the oscillator. In addition, it is effective to increase the load Q factor of the oscillator in order to reduce the phase noise. For example, increasing the Q factor ten times can reduce the phase noise by 1/100.
Thus, using an dielectric material having a high Q factor for the material of the oscillator and shaping precisely the oscillator so as to have a desired resonant frequency, the adhesive agent with a low dielectric constant and a low dielectric loss is coated on another substrate so as to establish the electro-magnetic coupling of the resonator to the micro-strip transmission line formed on the surface connected to the oscillation part in high-frequency mode, or to the micro-strip transmission line formed on the surface of another substrate connected to the oscillation part in high-frequency mode, and then, the resonator is mounted precisely on the surface of another substrate by the precision mounter.
This kind of technology is disclosed, for example, “Millimeter-wave DRO with Excellent Temperature Stability of Frequency” in European Microwave Conference—Munich 1999, pp.197-200, and “A novel millimeter-wave multiplayer IC with planer TE010 mode dielectric resonator” in 1998 Asia-Pacific Microwave Conference, pp. 147-150.
As disclosed in Japanese Patent Laid-Open Number 10-31219 (1998), Microwave Monolithic Integrated Circuit having a built-in dielectric resonator is known. This is known as such a method that the resonator formed with a high Q factor dielectric material is embedded into the concave part formed on the surface of the substrate of the high-frequency integrated circuit.
In the prior art of the adhesive bonding method in which the resonator is bonded to the micro-strip transmission line connected to the oscillation part so as to establish the electro-magnetic coupling, there is such a problem that it is difficult to determine the shape of the resonator and its relative position to the micro-strip transmission line in order to satisfy the desired frequency and power as well as the designated phase noise.
As it is required that the precision for the geometrical dimension of the resonator to its designed target value is ±0.1% and that the precision for fixing the resonator to its designed position is ±5% of its geometrical dimension, as for the shape, it is necessary to trim the shape of the resonator by grinding the dielectric material, and as for the positioning, it is necessary to mount the resonator by the high-precision mounter, and thus, it has been difficult to operate the mass production and downsize the cost in production.
In the method disclosed in Japanese Patent Laid-Open Number 10-93219 (1998), as the device has such a structure as the integrated circuit, that is, MMIC accommodates the resonator, the size of MMIC is required to be larger than the size of the resonator. However, as the price per unit area of the materials such as GaAs used conventionally as the integrated circuit substrate in the high-frequency region is extremely high, it is difficult to produce the low-cost MMIC. In addition, as the dielectric constant in GaAs substrates is high as in about 13, its dielectric loss gets larger for the oscillator in which the resonator is embedded in the center of the substrate. In this case, as the Q factor as the oscillator is reduced due to the dielectric loss even in the fact of using the dielectric material with high Q factor for the resonator, there is such a problem that the expected effect of high Q factor is not attained.